MECHANISM OF FORMATION OF FREEZE-THAW LOESS LANDSLIDES IN ILI REGION

Ili region is a typical seasonal permafrost area. The development of freeze-thaw loess landslides is strong,causing great potential danger to the safety of people's lives and properties. In this paper,we take the frozen-thawed loess landslide in Karaya Gaqi Township,Yining County,as the research object,and use the means of on-site field investigation,in-situ ground temperature monitoring,indoor experiment and numerical simulation method to carry out the research on the formation mechanism of frozen-thawed loess landslide. By analyzing the developmental characteristics and influencing factors of freeze-thaw loess landslides in the study area,it is confirmed that the top soil layer of loess landslides is subject to the long-term influence of freeze-thaw cycle action,and the seasonal freeze-thaw cycle in the study area is summarized into four stages: unfrozen period,alternating freezing period,freezing period,and thawing period. The test results show that the cohesion of the original loess is greatly affected by the number of freeze-thaw cycles,and the decrease reaches the maximum at 4 times of freeze-thaw cycles,and finally the cohesion has a tendency to level off. With the increase of the number of freeze-thaw cycles,the angle of internal friction shows a tendency to decrease,but the decrease is small,and the influence of the degree is in the range of 3°~5°. The simulation results show that the freezing hysteresis effect of freeze-thaw loess landslides is significant,and the stability of landslides increases instead of decreasing during the freezing period due to the greater strength of the frozen layer,and the stability of the slopes decreases abruptly when the initial thawing stage is at the most unstable stage in the whole freeze-thaw process. The study shows that the formation of freeze-thaw loess landslide is affected by both freeze-thaw cycle and freezing hysteresis.